The present invention relates to a control method/system for controlling vehicle starting (i.e., vehicle launch) in an at least partially automated mechanical transmission system. In particular, the present invention relates to the control of starting in a vehicular automated mechanical transmission system wherein the system senses conditions indicative of a vehicle launch, such as very low vehicle ground speed and a less-than-fully engaged master clutch, and limits maximum engine speed until substantially full clutch engagement is sensed.
Fully or partially automated mechanical transmission systems for vehicular use are known in the prior art, as may be seen by reference to U.S. Pat. Nos. 4,361,060; 4,648,290; 4,722,248; 4,850,236; 5,389,053; 5,487,004; 5,435,212 and 5,755,639.
Controls for automated mechanical transmission systems, especially wherein dynamic shifting is accomplished while maintaining the master clutch engaged and/or wherein the master clutch is manually controlled and is disengaged only for starting or stopping the vehicle, are known in the prior art, as may be seen by reference to U.S. Pat. Nos. 4,576,065; 4,916,979; 5,335,566; 5,425,689; 5,272,939; 5,479,345; 5,533,946; 5,582,069; 5,582,558; 5,620,392; 5,489,247; 5,490,063 and 5,509,867, the disclosures of which are incorporated herein by reference.
The prior art systems, especially the prior art systems having manually controlled clutch pedals used for starting, provided the opportunity for abuse of the driveline if the driver, when starting, fully depressed the throttle and then quickly released the clutch. Such xe2x80x9cpoppingxe2x80x9d of the clutch could cause undue wear and/or damage to the various components of the vehicle driveline.
This invention relates to a control for a vehicular automated mechanical transmission system which will sense conditions indicative of vehicle launch and will protect the vehicle from shocks until the master clutch is fully or substantially fully engaged. The foregoing is accomplished in a system wherein operating conditions are sensed/determined and engine speed (ES) controlled by sensing vehicle start conditions (i.e., if the vehicle ground speed is low (OS less than REF), the transmission is engaged in a gear ratio, the throttle is depressed (THL greater than REF), and if the master clutch is not fully engaged, then engine speed is governed to a maximum speed equal to about 200-300 RPM above idle (ES less than ESIDLE+300 RPM)).
The above control logic will minimize large driveline shocks caused by rapidly engaging (xe2x80x9cpoppingxe2x80x9d) the master clutch at high engine speeds and also provides a handy engine speed governor for starting on grades. For example, when starting the vehicle on a grade, or in other highly loaded situations, the driver could fully depress the accelerator and then slowly let out the clutch. When the clutch becomes fully locked up, the engine speed control is ended and the vehicle accelerates normally. This allows the driver to use a higher engine speed to get started in a difficult condition while retaining the benefits of the electronic speed limit control. In a hill-start condition, the driver could also use the trailer brakes, or another hill-start aid, to hold the vehicle from rolling backward during the start.
Accordingly, an improved start control for automated mechanical transmissions is provided that will minimize driveline shocks due to clutch xe2x80x9cpoppingxe2x80x9d and will provide good start-on-grade performance.
In another aspect of the invention, a system and method of controlling a vehicular automated transmission system is disclosed. The method comprises the steps of:
(a) determining a maximum starting gear of the system when a Gross Combination Weight (GCW) of the vehicle is known by the system; and
(b) limiting the maximum starting gear of the system to a fully laden vehicle when the GCW of the vehicle is not known by the system.
In addition, the method includes the steps of determining an allowed start gear ratio when insufficient vehicle acceleration is being detected by the system and forcing a downshift of the transmission until the system detects sufficient vehicle acceleration. Further, the method includes the steps of determining the power transmitted through the clutch by using the transmission input speed, the engine speed and the torque at a flywheel, and limiting one of engine torque and engine speed when excessive power through the clutch is detected by the system.
The system of the invention includes a microprocessor to process input signals in accordance with logic rules to issue command output signals to transmission system actuators. Specifically, the microprocessor receives a first input corresponding to a predetermined weight of the vehicle, a second input corresponding to a starting gear ratio of the system when the predetermined weight of the vehicle is known by the system, and generates an output signal limiting the maximum starting gear ratio of the system to a fully laden vehicle when the predetermined weight of the vehicle is not known by the system. In addition, an allowed start gear ratio of the system is determined when insufficient vehicle acceleration is being detected by the system and a downshift of the transmission is forced until the system detects sufficient vehicle acceleration. The system also determines the power transmitted through the clutch and limits the engine torque and/or engine speed to a preset value when excessive power through the clutch is detected by the system.
Various aspects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.